1. Field of the Invention
The present invention relates to a paint composition whose storage stability is high. Moreover, it relates to a wear-resistant coating film which uses the paint composition and is good in terms of the adherence, and a process for producing the wear-resistant coating film.
2. Description of the Related Art
Plastic materials are lightweight, can be formed with ease, and are good in terms of the shock-resistance and transparency. Accordingly, they offer a wide range of applications. However, since they are likely to be damaged by wear, they lose the glossiness and transparency in service. Hence, as a method for reforming the surface of plastic materials, it has been carried out forming coating films on the surface of plastic materials by treating with hard coating agents. Among the hard coating agents, silicone hard coating paints containing a variety of silicone compounds have been well known.
Many silicone hard coating paints have been developed so far. For example, Japanese Unexamined Patent Publication (KOKAI) No. 8-238,683 discloses a hard coating agent in which a silane compound and/or the hydrolyzed products serve as a binder, and which contains surface-coated fine particles of titanium oxide and aluminum perchlorate. Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 62-195,061 discloses a primer which is produced by co-polymerizing titanium alkoxide and a silane compound.
However, when silicone hard coating paints are produced by partially hydrolyzing silane compounds or metallic alkoxides and condensing them by dehydration to synthesize oligomers with appropriate sizes, it is difficult to inhibit the resulting oligomers from growing furthermore. Accordingly, the oligomers grow with time to such a size that they are not applicable to paints. Thus, conventional silicone hard coating paints generally exhibit poor storage stability. Moreover, when metallic alkoxides are hydrolyzed and condensed by dehydration, the hydrolysis and dehydration condensation accompanies dealcoholization. However, since the resulting alcohols have a non-negligible volume with respect to molecules making paints, they cause the cure shrinkage which sharply reduces the volume of paints after curing, and are accordingly the causes of come-off or cracked paint films. The cure shrinkage occurs remarkably when the thickness of paint films is thicker. On the contrarily, when the thickness of paint films is thinner, paint films have a problem with the strength.
Moreover, Japanese Unexamined Patent Publication (KOKAI) No. 6-200,034, Japanese Unexamined Patent Publication (KOKAI) No. 7-126,396 and Japanese Unexamined Patent Publication (KOKAI) No. 9-241,380 disclose layer organic-inorganic composites. The layer organic-inorganic composites can be used as coating materials, and have the characteristics of inorganic materials and organic materials simultaneously. However, since layer organic silicone polymers are cured by reacting and bonding organic functional groups, the coating materials are limited in view of the hardness.